Costs of compliance could be in the tens of billions of dollars, but the government said the rules would save other billions — as well as lives — in the long run.

More than 300 counties — mainly in southern California, the Northeast and Gulf Coast — already violate the requirements adopted two years ago by the Bush administration and will find it even harder to reduce smog-forming pollution enough to comply with the law.

The new limits being considered by the Environmental Protection Agency could more than double the number of counties in violation and reach places such as California’s wine country in Napa Valley and rural Trego County, Kan., and its 3,000 residents.

As many as nine of Maine’s 16 counties might be forced to find ways to clamp down on smog-forming emissions from industry and automobiles or face government sanctions, most likely the loss of federal highway dollars.

According to a three-year average recorded by EPA from 2006 to 2008, air quality levels in Hancock and York counties in Maine failed to meet the Bush standard. But under the stricter limits Obama’s administration is considering, Washington, Penobscot, Oxford, Knox, Kennebec, Cumberland and Androscoggin counties could join them.

Click here for a chart showing ozone concentrations in those counties.

For the first time, counties in Idaho, Nevada, Oregon, the Dakotas, Kansas, Minnesota and Iowa might fail air quality tests.

The tighter standards, though costly to implement, ultimately will save billions in avoided emergency room visits, premature deaths, and missed work and school days, the EPA said.

“EPA is stepping up to protect Americans from one of the most persistent and widespread pollutants we face,” said EPA Administrator Lisa Jackson. “Using the best science to strengthen these standards is long overdue action that will help millions of Americans breathe easier and live healthier.”

The proposal presents a range for the allowable concentration of ground-level ozone, the main ingredient in smog, from 60 parts per billion to 70 parts, as recommended by scientists during the Bush administration. That’s equivalent to a single tennis ball in an Olympic-sized swimming pool full of tennis balls.

EPA plans to select a specific figure within that range by August. Counties and states then will have up to 20 years to meet the new limits, depending on how severely they are out of compliance. They will have to submit plans for meeting the new limits by the end of 2013 or early 2014.

Former President George W. Bush personally intervened in the issue after hearing complaints from electric utilities and other affected industries. His EPA set a standard of 75 parts per billion, stricter than one adopted in 1997 but not as strict as what scientists said was needed to protect public health.

Some of those same industries reiterated their opposition Thursday to a stronger smog standard.

“We probably won’t know for a couple of years just what utilities and other emissions sources will be required to do in response to a tighter ozone standard,” said John Kinsman, a senior director at the Edison Electric Institute, an electric industry trade group. “Utilities already have made substantial reductions in ozone-related emissions.”

Parts of the country that already have spent decades and millions of dollars fighting smog and still are struggling to meet existing thresholds questioned what more they could do. They already have cut pollution from the easier sources by increasing monitoring and enforcement and requiring car emissions tests.

“This EPA decision provides the illusion of greater protectiveness, but with no regard for cost, in terms of dollars or in terms of the freedoms that Americans are accustomed to,” said Bryan W. Shaw, chairman of the Texas Commission on Environmental Quality. Texas, with its heavy industry, is home to Houston, one of the smoggiest cities in the nation.

Environmentalists endorsed the new plan. “If EPA follows through, it will mean significantly cleaner air and better health protection,” said Frank O’Donnell, president of the advocacy group Clean Air Watch.

EPA estimates meeting the new requirements will cost industry and motorists from $19 billion to as much as $90 billion a year by 2020. The Bush administration had put the cost of meeting its threshold at $7.6 billion to $8.5 billion a year.

The new regulations would mean more controls on large industrial facilities, plus regulating smaller facilities and sources. New federal regulations in the works to improve car and truck fuel economy and curb global warming pollution at large factories also will help communities meet any new standards, the EPA said.

Smog is a respiratory irritant that has been linked to asthma attacks and other illnesses. Global warming is expected to make it worse, since smog is created when emissions from cars, power and chemical plants, refineries and other factories mix in sunlight and heat.

But some parts of the country that could be found in violation of the proposed standards have very few cars and little industry. In places such as these, smog-forming pollution is being blown in from hundreds of miles away.

Charlene Neish, director of Trego County Economic Development, moved to the rural county in western Kansas a decade ago from Phoenix to escape big city problems such as traffic and air pollution. Neish was shocked that her county, which has about nine people per square mile and virtually no industry, made the list.

In Utah, six more counties would join the three in violation of the Bush standard.

Cheryl Heying, director of Utah’s Division of Air Quality, said the change will not only require additional reductions in vehicle and industrial emissions, but a regional focus on other contributors such as wildfire smoke and offshore shipping.

“That doesn’t mean we’re just going to point our finger at everyone else, but if we don’t cooperate, we’re never going to get it done,” Heying said.